This project's long term goal is to determine the mechanism of action of electrically driven amino acid, potassium ion cotransport (symport) of insects, to assess its role in K+ homeostasis, and to identify symport inhibitors. The working hypothesis is that the twenty naturally occurring L-amino acids, AAs, move from highly alkaline midgut contents to neutral across brush border membranes. Identification, isolation, and determination of the primary structure of the symporter proteins are required to reach the goal. Brush border membrane vesicles, BBMV, isolated from feeding, fifth instar larvae of the tobacco hornworm, Manduca sexta, will be used to study AA uptake by rapid filtration and fluorescence quenching techniques. Three aims lead naturally toward the goal. In Aim 1 symporter substrate sub-groups are identified through cation-gradient and counter-transport studies of AA-K+ uptake using labeled AA, rapid filtration techniques. These techniques have been used successfully to study AA uptake kinetics in eel BBMV but are novel in the study of insects. In Aim 3 high affinity amino acid analogues are identified and used to label symport proteins. The project will pave the way for isolating symporter proteins, for cloning symporter cDNA, and for determining the primary structure of the proteins. AA analogues which interfere with AA-K+ symporter proteins in Lepidoptera may be developed as environmentally safe agents for insect control. The extremely high lumen pH (approaching 11.5) and positive PD (approaching 240 mV) of Lepidopteran midgut may be reflected in unusual AA-cation symporters, unlike those of mammals and birds. Since larval mosquito midguts also have high lumen pH, such AA symport-inhibiting analogues may be selectively toxic to mosquito larvae and be useful in disease vector control.